The content of pesticides in those plants which are intended to be used for outaining of drug is, in many countries, limited by stringent regulations and is one of the most important criteria for the commercial usefulness of drugs. Therefore, the removal of pesticides from these drugs with the simultaneous maintenance of the full activity spectrum is of great interest, especially when it is a question of very valuable materials.
A prerequisite for a removal of these undesired pesticides by means of extraction with a solvent is that the extraction is sufficiently selective, i.e. only the undesired substances are extracted, and, on the other hand, after the extraction the drug is also present in a useable condition, i.e. is free from undesired residues of solvents. It is known that a high pressure extraction with supercritical carbon dioxide fulfils this latter prerequisite.
Thus, for example, German Offenlegungschrift No. 36 32 401 describes the production of hop extracts with a low content of pesticides from hops which are laden with pesticides. In that process, in a first step, the pesticides and the component materials of the hops are extracted with compressed gases and, in a subsequent step, there is carried out a separation of extract and pesticides with the aid of a solid adsorption agent. However, a complete extraction of the pesticides from the hops is not desired since the extract is to be further used. A further disadvantage is the insufficient selectivity of the adsorption agent since, besides the pesticides, desired hop component materials are also bound and thus the yields are reduced.
Furthermore, from "Verdichtet Gase zur Extraktion und Raffination", pub. by Springer Verlag, pp. 231-233/1987, it is known to remove pesticides from senna leaves with dry, supercritical carbon dioxide in which case the content of chlorinated pesticides is reduced by up to 98% without the polar active materials, the sennosides, being co-extracted.
However, the application of the process which is successful in the case of senna leaves to ginseng roots has proved to be impossible. The ginsenosides, regarded as being the active materials, are admittedly not extracted with supercritical carbon dioxide but the chlorinated pesticides are also not removed in a satisfactory manner. Thus, for example, quintozene (pentachloronitrobenzene), which is to be regarded as being the main contamination of ginseng roots and thus as a leading substance for undesired, lipophilic, chlorinated pesticides, is only reduced to about 30% so that the extracted ginseng roots do not even approach the region of commercial usefulness when the pesticide content thereof exceeds the permitted value by a factor of 100, which can certainly occur.